The present invention relates to a magnetic pump, in which a rotator, consisting of an impeller and a magnetic can, is rotatably supported by a supporting shaft and the magnetic can is rotationally driven from the outside of a rear casing.
In such the magnetic pump, a front casing forms a pump space and a rear casing forms a cylindrical space extending from the pump space. Arranged in the cylindrical space of the rear casing is a cylindrical magnetic can that is rotatably supported by a supporting shaft of which one end is secured on the rear casing. A rotary driving means, magnetically coupled to the magnetic can via the rear casing, is located outside the magnetic can to rotate the magnetic can with a driving force from the rotary driving means. The magnetic can is integrally coupled to an impeller that is accommodated in the pump space. When the impeller rotates, a fluid to be pumped is drawn into inside the pump space through an inlet located at the front of the front casing and then the fluid is discharged through an outlet located at a side of the front casing.
The following methods are employed in the art to couple the magnetic can with the impeller. (1) The impeller and the magnetic can are press-fitted or frictionally secured with each other using a cushion member. (2) The impeller and the magnetic can are coupled to each other with a screw. (3) The impeller and the magnetic can are coupled to each other with a weld.
The rotator consisting of the magnetic can and the impeller is supported on the supporting shaft by a cylindrical rotary bearing. The rotary bearing is movable in the thrust direction. During normal runs, when the fluid is pumped, the rotator totally slides forward because the inlet is negatively pressurized. During idling runs when the fluid is not present and abnormal runs such as an air involving run, the rotator totally slides backward because of a magnetic attractive force between the magnetic can and the rotary driving means. As a result, the rear surface of the rotary bearing contacts a thrust bearing of a casing opposite to that surface.
The magnetic pump mentioned above has several disadvantages in its reliability. First, it is difficult to maintain a stable state of coupling between the magnetic can and the impeller for a long term. For example, in the above method (1), the impeller possibly separates from the magnetic can due to the lowered coupling force reduced in accordance with an elapsed time or when a liquid at a high temperature is pumped. In the coupling method (2), the coupling portion is loosen by an inertial force when the pump is rotated erroneously or when the pump is stopped, thereby resulting in a possibility that separates the impeller from the magnet. In the coupling method (3), disadvantageously, it takes a long production time and moreover it is impossible to change parts once assembled.
Second, in the magnetic pump mentioned above, at the times of initial driving and abnormal runs such as idling and air involving runs, the rear end of the bearing of the rotator contacts the rear thrust bearing. As a result, the pump is possibly broken due to an impact at that moment and a sliding heat between the rear thrust bearing and the bearing end.
The present invention has been made in consideration of the above disadvantages and accordingly has a general object to provide a magnetic pump with an improved reliability.
More specifically, the present invention has an object to provide a magnetic pump capable of maintaining a stable state of coupling between an impeller and a magnetic can for a long term, in which parts can be changed individually with ease.
Moreover, the present invention has another object to provide a magnetic pump that is not damaged due to a heat and an impact at the times of idling and abnormal running such as air involving.
The present invention is provided with a magnetic pump, comprising: a front casing forming an interior pump space and having an inlet for drawing in a fluid to be pumped and an outlet for discharging the fluid; a rear casing for forming a cylindrical space extending from the pump space; a supporting shaft arranged in the cylindrical space and having a rear end supported by a rear end of the rear casing and a front end facing to the pump space; a totally cylindrical magnetic can rotatably supported by the supporting shaft and having an inner circumference on which a cylindrical rotary bearing is mounted and an outer circumference on which a driven magnet is mounted; an impeller secured on a front end of the magnetic can and accommodated in the pump space so as to rotate integrally with the magnetic can; a rotary driving means magnetically coupled to the driven magnet via the rear casing for supplying a rotary driving force to the impeller via the driven magnet; a rear bearing arranged at a rear end of the rotary bearing; and a rear thrust bearing arranged at a portion opposite to the rear bearing of the rear casing for contacting the rear bearing when the rotary bearing moves backward during an abnormal run of the pump, wherein the magnetic can and the impeller are fitted with each other in the axial direction and coupled by a pin passing through both in the radial direction.
According to the present invention, the magnetic can is coupled to the impeller by a pin that passes through both in the radial direction. Therefore, the coupling force at the coupled portion is not lowered with aging and heating as well as an inertial force when the pump inversely rotates or stops. In addition, according to the present invention, the magnetic can is coupled to the impeller in the axial and rotational directions by a pin. Therefore, both can be easily decomposed/assembled and their parts are individually changeable.
Preferably, a coupling interface between the magnetic can and the impeller comprises a surface extending in the radial direction for transmitting a rotary driving force. In such the arrangement, the rotary driving force transmitting surface mainly secures the impeller with the magnetic can in the rotational direction (the direction in which the driving force is transmitted). Therefore, an excessively large load cannot impart on the pin, which can be thinned and downsized to that extent.
In addition, the pin may be inserted through the magnetic can and the impeller from the inner circumference to the outer circumference and it may be protected by the outer circumference of the rotary bearing not to be pulled out. In such the arrangement, once the magnetic can and the impeller are assembled, the pin can not be pulled out easily and can maintain a stable state of coupling.
The present invention is also provided with a magnetic pump, comprising: a front casing for forming an interior pump space and having an inlet for drawing in a fluid to be pumped and an outlet for discharging the fluid; a rear casing for forming a cylindrical space extending from the pump space; a supporting shaft arranged in the cylindrical space and having a rear end supported by a rear end of the rear casing and a front end facing to the pump space; a totally cylindrical magnetic can rotatably supported by the supporting shaft and having an inner circumference on which a cylindrical rotary bearing is mounted and an outer circumference on which a driven magnet is mounted; an impeller secured on a front end of the magnetic can and accommodated in the pump space so as to rotate integrally with the magnetic can; a rotary driving means magnetically coupled to the driven magnet via the rear casing for supplying a rotary driving force to the impeller via the driven magnet; a rear bearing arranged at a rear end of the rotary bearing; and a rear thrust bearing arranged at a portion opposite to the rear bearing of the rear casing for contacting the rear bearing when the rotary bearing moves backward during an abnormal run of the pump, wherein one of the rear bearing and the rear thrust bearing has such a cross section that reduces a sliding area.
According to the present invention, either the rear bearing that is located at the rear end of the rotary bearing or the rear thrust bearing that contacts the rear bearing has such a cross section that reduces a sliding area (for example, a tapered cross section). Therefore, a sliding heat between the rear bearing and the rear thrust bearing can be suppressed lower than that in the art enough to prevent an excessive heat. In addition, a total surface area increases at portions that do not slide. Therefore, a heat from the sliding portion can be dissipated efficiently more than a flat bearing. This can improve durability during abnormal runs.
A cushion member for shock absorbing may be interposed between the rear bearing and the rotary bearing. This can relieve an impact between the rear bearing and the rotary bearing when they contact with each other during abnormal runs and can prevent the pump from being damaged with the impact.
Furthermore, the rear bearing may have fans formed on a side opposite to the rear thrust bearing for supplying as a cooling liquid the fluid to a sliding portion between the rear bearing and the rear thrust bearing. The cooling liquid can be circulated by force to the sliding portion of the bearing to further improve a cooling effect.